Light generating microcapsules for self-healing polymer applications

ABSTRACT

A self-healing polymeric material includes a polymeric matrix material, wherein dispersed within the polymeric matrix material is a mixture of materials that includes monomers and a photoinitiator, and a plurality of light generating microcapsules dispersed in the polymeric matrix material. Each light generating microcapsule encapsulates multiple reactants that undergo a chemiluminescent reaction. The chemiluminescent reaction generates a photon having a wavelength within a particular emission range that is consistent with an absorption range of the photoinitiator.

BACKGROUND

Typical self-healing polymers utilize encapsulated monomers that reactin the presence of a catalyst that is incorporated into the polymermatrix. The healing material is limited in selection because a propermonomer/catalyst pair must be compatible with the polymer matrix.Additionally, self-healing schemes typically involve thermally initiatedreactions. In some cases (e.g., outdoor applications with low ambienttemperatures), such thermally initiated reactions may proceed too slowlyto repair damage at an early stage.

SUMMARY

According to an embodiment, a self-healing polymeric material isdisclosed that includes a polymeric matrix material, wherein dispersedwithin the polymeric matrix material is a mixture of materials thatincludes monomers and a photoinitiator, and a plurality of lightgenerating microcapsules dispersed in the polymeric matrix material.Each light generating microcapsule encapsulates multiple reactants thatundergo a chemiluminescent reaction. The chemiluminescent reactiongenerates a photon having a wavelength within a particular emissionrange that is consistent with an absorption range of the photoinitiator.

According to another embodiment, a process of utilizingchemiluminescence for polymeric self-healing is disclosed. The processincludes dispersing a monomer mixture in a polymeric matrix material.The monomer mixture is a mixture of materials that includes monomers anda photoinitiator. The process also includes dispersing a lightgenerating microcapsule in the polymeric matrix material. The lightgenerating microcapsule encapsulates multiple reactants that undergo achemiluminescent reaction. The chemiluminescent reaction generates aphoton having a wavelength within a particular emission range that isconsistent with an absorption range of the photoinitiator. The lightgenerating microcapsule is adapted to cause the multiple reactants toundergo the chemiluminescent reaction within the light generatingmicrocapsule in response to application of a compressive force.

According to another embodiment, an in-situ light generation process isdisclosed that includes forming an article of manufacture that includesa self-healing polymeric material. The self-healing polymeric materialincludes a polymeric matrix material, wherein dispersed within thepolymeric matrix material is a mixture of materials that includesmonomers and a photoinitiator, and a plurality of light generatingmicrocapsules dispersed in the polymeric matrix material. Each lightgenerating microcapsule encapsulates multiple reactants that undergo achemiluminescent reaction. The chemiluminescent reaction generates aphoton having a wavelength within a particular emission range that isconsistent with an absorption range of the photoinitiator. The processalso includes exposing the article of manufacture to an environment thatresults in formation of a crack in the polymeric matrix material. Thecrack causes migration of the mixture of materials into the crack. Thechemiluminescent reaction within the light generating microcapsulegenerates sufficient light to cause the photoinitiator to initiate apolymerization reaction of the monomers within the crack. Thepolymerization reaction results in formation of a polymeric materialthat seals the crack.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescriptions of exemplary embodiments of the invention as illustrated inthe accompanying drawings wherein like reference numbers generallyrepresent like parts of exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of selected portions of an article ofmanufacture that utilizes light generating microcapsules for polymericself-healing, according to one embodiment.

FIG. 2A is a cross-sectional view of a multiple-compartment microcapsulecorresponding to one of the light generating microcapsules depicted inFIG. 1, in which reactants that undergo a chemiluminescent reaction areisolated within individual compartments of the microcapsule, accordingto one embodiment.

FIG. 2B is a cross-sectional view of the multiple-compartmentmicrocapsule of FIG. 2A after a compressive force results in rupture ofan inner compartment of the microcapsule to enable the reactants toundergo the chemiluminescent reaction within the microcapsule, accordingto one embodiment.

FIG. 3A is a cross-sectional view of selected portions of the article ofmanufacture of FIG. 1 at a first stage of propagation of a crack in theself-healing polymeric matrix material, according to one embodiment.

FIG. 3B is a cross-sectional view of selected portions of the article ofmanufacture of FIG. 1 at a second stage of propagation of the crackresulting in rupture of a monomer mixture microcapsule and release of amonomer mixture (that includes monomers and a photoinitiator) to fillthe crack, according to one embodiment.

FIG. 3C is a cross-sectional view of selected portions of the article ofmanufacture of FIG. 1 at a third stage of propagation of the crackcausing a compressive force to a light generating microcapsule resultingin a chemiluminescent reaction with a photon emission wavelength that issatisfactory to excite the photoinitiator in order to initiatepolymerization of the monomers to seal the crack, according to oneembodiment.

FIG. 4 is a flow diagram illustrating a method of producing amultiple-compartment microcapsule having a shell-in-shell architecturewith an inner shell contained within an outer shell, where the innershell is adapted to rupture in response to application of a compressiveforce to cause a chemiluminescent reaction within the microcapsule,according to some embodiments.

DETAILED DESCRIPTION

The present disclosure describes light generating microcapsules andprocesses of utilizing the light generating microcapsules for in-situgeneration of light for self-healing polymeric applications.Chemiluminescence is the emission of photons as the result of a chemicalreaction. In the present disclosure, a light generating microcapsuleincludes multiple compartments to isolate a first reactant (or a firstset of reactants) from a second reactant (or a second set of reactants)within the same microcapsule. Application of a particular stimulus(e.g., a compressive force) to the multiple-compartment microcapsuleresults in rupture of an inner compartment, enabling the firstreactant(s) and the second reactant(s) to mix and undergo achemiluminescent reaction within the microcapsule.

The light generating microcapsules of the present disclosure may bedispersed within a polymeric matrix material (also referred to herein asa “self-healing polymeric matrix material”) to enable photons to begenerated in situ within the polymeric matrix material. In someembodiments of the present disclosure, the polymeric matrix materialfurther includes a second set of microcapsules (also referred to hereinas “monomer mixture microcapsules”) that encapsulate a mixture ofmaterials that includes monomers and a photoinitiator. Thephotoinitiator may create reactive species (e.g., free radicals,cations, or anions) when exposed to radiation (e.g., UV or visiblelight). In a particular embodiment, the photoinitiator may correspond toa free radical initiator to initiate a free-radical polymerizationreaction. In alternative embodiments, rather than utilizingmicrocapsules to encapsulate the mixture, the monomers and thephotoinitiator may be dispersed throughout the polymeric matrixmaterial.

As illustrated and described further herein with respect to FIGS. 3A-3C,propagation of a crack in the self-healing polymeric matrix materialresults in rupture of a monomer mixture microcapsule (or multiplemicrocapsules), causing the monomers and the photoinitiator to fill thecrack. Further propagation of the crack results in application of acompressive force to a light generating microcapsule (or multiplemicrocapsules), triggering the chemiluminescent reaction within thelight generating microcapsule. An outer shell of the light generatingmicrocapsule may be formed from a material that enables a substantialportion of the photons generated within the microcapsule to exit intothe surrounding material(s), including the monomer mixture that hasfilled the crack. The emitted light is within a particular wavelengthrange that is satisfactory to excite the photoinitiator to createreactive species (e.g., free radicals) to trigger polymerization (e.g.,free radical polymerization) of the monomers that have filled the crack.Thus, in contrast to existing polymeric self-healing schemes thatinvolve a thermally initiated reaction, the light-triggered self-healingmechanism of the present disclosure enables polymeric self-healingwithout employing other means, such as an external heat source toaccelerate a thermally initiated reaction.

As used herein, the term “light” is used to refer to ultraviolet (UV)light (in a wavelength range of 10 nm to 400 nm), visible light (e.g.,in a wavelength range of 400 nm to 700 nm), or infrared light (e.g.,above 700 nm) that may be produced as a result of a chemiluminescentreaction. As used herein, the term “microcapsule” is used to refer tocapsules that are in a range of about 10 microns to 1000 microns indiameter. However, it will be appreciated that the following disclosuremay be applied to capsules having a smaller size (also referred to as“nanocapsules”).

FIG. 1 illustrates a cross-sectional view of selected portions of anarticle of manufacture 100 that utilizes light generating microcapsules102 for polymeric self-healing, according to one embodiment. In FIG. 1,a self-healing polymeric matrix material 104 includes a plurality of thelight generating microcapsules 102 and a plurality of monomer mixturemicrocapsules 106 dispersed therein. The monomer mixture microcapsules106 may encapsulate a mixture of monomers (e.g., acrylate monomers) anda photoinitiator (e.g., a free radical initiator). As illustrated andfurther described herein with respect to FIGS. 3A-3C, propagation of acrack in the self-healing polymeric matrix material 104 may result inrupture of at least one of the monomer mixture microcapsules 106,causing the encapsulated mixture (including the photoinitiator) to fillthe crack. Further propagation of the crack results in application of acompressive force to at least one of the light generating microcapsules102, triggering a chemiluminescent reaction within at least one of thelight generating microcapsules 102. The emitted photons are within aparticular wavelength range that is satisfactory to cause thephotoinitiator to generate free radicals to initiate polymerization ofthe monomers to “heal” the self-healing polymeric matrix material 104 byforming a polymerized material that seals the crack.

In FIG. 1, the monomer mixture microcapsules 106 are shown prior to theformation of a crack in the self-healing polymeric matrix material 104that results in rupture of at least one of the monomer mixturemicrocapsules 106, causing the encapsulated mixture to fill the crack.As illustrated and further described herein with respect to FIGS. 3A and3B, a crack in the self-healing polymeric matrix material 104 may resultin the rupture of one (or more) of the monomer mixture microcapsules 106and the release of the encapsulated monomer mixture into the crack. Asillustrated and further described herein with respect to FIG. 3C, thephotons generated within one (or more) of the light generatingmicrocapsules 102 may excite the photoinitiator (e.g., a free radicalinitiator) to initiate a polymerization reaction (e.g., a free radicalpolymerization reaction) to form a cross-linked material that seals thecrack, thereby preventing further propagation of the crack.

The monomers encapsulated within the monomer mixture microcapsules 106may correspond to an acrylate monomer, an epoxide monomer, or anothertype of monomer that undergoes a particular type of polymerizationreaction triggered by the photoinitiator (e.g., a free radicalpolymerization reaction in the case of a free radical initiator). Themonomers begin to polymerize as the photoinitiator is energized byradiation from a chemiluminescent light source.

The light generating microcapsules 102 illustrated in FIG. 1 includemultiple compartments and are also referred to herein asmultiple-compartment microcapsules. In FIG. 1, the light generatingmicrocapsules 102 are shown prior to application of a compressive forcethat results in a chemiluminescent reaction within the individual lightgenerating microcapsules 102. Accordingly, FIG. 1 illustrates that thecompartments of the light generating microcapsules 102 enable isolationof reactants in order to prevent the chemiluminescent reaction prior toapplication of the compressive force.

In the particular embodiment depicted in FIG. 1, the light generatingmicrocapsules 102 dispersed in the self-healing polymeric matrixmaterial 104 have a shell-in-shell architecture with an inner shellcontained within an outer shell, where the inner shell is adapted torupture in response to application of a compressive force in order totrigger a chemiluminescent reaction within the light generatingmicrocapsules 102. Thus, the individual light generating microcapsules102 depicted in FIG. 1 may correspond to the multiple-compartmentmicrocapsule (having a shell-in-shell architecture) formed according tothe process described herein with respect to FIG. 4. It will beappreciated that, in alternative embodiments, the light generatingmicrocapsules 102 may have an alternative multiple-compartmentmicrocapsule design, may include more than one type ofmultiple-compartment microcapsule design, or a combination thereof.

As described further herein, the chemiluminescent reaction generatesactinic photons within a particular wavelength range that issatisfactory to excite a particular photoinitiator to initiatepolymerization of the monomers. The outer shell of the light generatingmicrocapsules 102 allows a substantial portion of the actinic photonsgenerated within the microcapsules 102 as a result of thechemiluminescent reaction to pass through the outer shell into thesurrounding material(s). As described further herein with respect toFIG. 4, the outer shell can be made from chemically non-reactivematerials, such as some plastics which are transparent, translucent, orlight filtering to pass the appropriate wavelengths of light into thesurrounding material(s). In a particular embodiment, the outer shell hasa transmittance value of at least 90% for the particular emitted photonwavelength(s). In certain embodiments, the outer shell may include anatural polymeric material, such as gelatin, arabic gum, shellac, lac,starch, dextrin, wax, rosin, sodium alginate, zein, and the like;semi-synthetic polymer material, such as methyl cellulose, ethylcellulose, carboxymethyl cellulose, hydroxyethyl ethyl cellulose;full-synthetic polymer material, such as polyolefins, polystyrenes,polyethers, polyureas, polyethylene glycol, polyamide, polyurethane,polyacrylate, epoxy resins, among others.

Thus, FIG. 1 illustrates an example of an article of manufacture thatincludes light generating microcapsules dispersed in a polymeric matrixmaterial to enable self-healing of the polymeric matrix material. Asillustrated and further described herein with respect to FIGS. 3A-3C,propagation of a crack in the polymeric matrix material causes themonomer mixture microcapsule(s) dispersed in the polymeric matrixmaterial to rupture and release the encapsulated monomer mixture(including the photoinitiator) into the crack. Further propagation ofthe crack results in application of a compressive force to the lightgenerating microcapsule(s) that triggers a chemiluminescent reactionwithin the light generating microcapsule(s). The chemiluminescentreaction emits light of sufficient energy to excite the photoinitiatorfor polymerization of the monomers that have filled the crack, thereby“healing” the polymeric matrix material by forming a polymerizedmaterial that seals the crack to prevent further propagation of thecrack.

FIG. 2A illustrates an exploded cross-sectional view 200 of amultiple-compartment microcapsule 202 corresponding to one of theplurality of the light generating microcapsules 102 depicted in FIG. 1,according to one embodiment. In FIG. 2A, the multiple-compartmentmicrocapsule 202 is shown prior to application of a compressive force tothe multiple-compartment microcapsule 202. In FIG. 2A, reactants thatundergo a chemiluminescent reaction are isolated within individualcompartments of the multiple-compartment microcapsule 202. Asillustrated and further described herein with respect to FIG. 2B,application of a compressive force to the multiple-compartmentmicrocapsule 202 depicted in FIG. 2A (e.g., as a result of a crack inthe self-healing polymeric matrix material 104) enables the isolatedreactants to mix and undergo the chemiluminescent reaction within themultiple-compartment microcapsule 202.

The exploded cross-sectional view 200 of FIG. 2A illustrates aparticular embodiment in which the multiple-compartment microcapsule 202has an outer wall 210 (also referred to herein as the “outer shell”) andcontains an inner microcapsule 212 and a first reactant 214 (or a firstset of multiple reactants). The inner microcapsule 212 has a capsulewall 216 (also referred to herein as the “inner shell”) and contains asecond reactant 218 (or a second set of multiple reactants). The firstreactant(s) 214 within the microcapsule 202 may surround the innermicrocapsule 212, and the first reactant(s) 214 may be prevented fromcontacting the second reactant(s) 218 by the capsule wall 216 of theinner microcapsule 212. In a particular embodiment, the capsule wall 216of the inner microcapsule 212 may be formed to rupture under aparticular compressive force, and the outer wall 210 of the microcapsule202 may be formed so as to not rupture under that compressive force.

FIG. 2B illustrates an exploded cross-sectional view 220 of theindividual multiple-compartment microcapsule 202 depicted in FIG. 2Aafter application of a compressive force to the multiple-compartmentmicrocapsule 202. FIG. 2B illustrates that compression of themultiple-compartment microcapsule 202 depicted in FIG. 2A results inrupture of the capsule wall 216 of the inner microcapsule 212 to allowthe first reactant(s) 214 and the second reactant(s) 218 to mix andundergo a chemiluminescent reaction 222. As described further hereinwith respect to FIG. 3C, a crack in the self-healing polymeric matrixmaterial 104 may result in rupture of the capsule wall 216 of the innermicrocapsule 212, allowing the reactants to mix and undergo thechemiluminescent reaction 222. FIG. 2B further illustrates that, in someembodiments, application of the compressive force does not result inrupture of the outer wall 210 of the multiple-compartment microcapsule202.

FIG. 2B illustrates that the chemiluminescent reaction 222 that occurswithin the microcapsule 202 generates light 224 (identified as “hv” inFIG. 2B), and the outer shell 210 of the microcapsule 202 allows asubstantial portion of the light 224 (or particular wavelength(s) of thelight 224) to pass through the outer shell 210 into the surroundingself-healing polymeric matrix material 104 (as well as into a crack thatis formed in the self-healing polymeric matrix material 104 and filledwith the monomer mixture, as shown in the example of FIG. 3C). Asdescribed further herein, the light 224 is within a particularwavelength range that is satisfactory to trigger a particularphotoinitiator to initiate polymerization (e.g., free radicalpolymerization) of the monomers that have filled the crack (as shown inFIGS. 3A and 3B) in order to prevent further propagation of the crack(as shown in FIG. 3C).

FIG. 2B further illustrates that the multiple-compartment microcapsule202 may contain a reaction product 226 of the reaction of the firstreactant(s) 214 and the second reactant(s) 218 (as shown in FIG. 2A). Asthe outer wall 210 may remain intact after application of thecompressive force, the outer wall 210 may prevent the reaction product226 from contacting the self-healing polymeric matrix material 104.

The chemical reaction diagram depicted in FIG. 2B represents anillustrative, non-limiting example of a chemiluminescent reaction thatmay occur within the light generating microcapsule 202. The examplechemiluminescent reaction depicted in FIG. 2B corresponds to a reactionof a suitable dye with diphenyl oxalate and a suitable oxidant such ashydrogen peroxide to produce a photon-emitting reaction. In a particularembodiment, the multiple-compartment microcapsule 202 may contain amixture of a dye and diphenyl oxalate in the inner microcapsule 212 asthe second reactant(s) 218 and may contain hydrogen peroxide as thefirst reactant(s) 214 surrounding the inner microcapsule 212. FIG. 2Billustrates that a product of a chemical reaction between diphenyloxalate and hydrogen peroxide is 1,2-dioxetanedione that has an unstablestrained ring, which decomposes spontaneously to carbon dioxide andreleases energy that excites a dye, and the excited dye subsequentlyreleases a photon as it returns to its ground state.

The top portion of the chemical reaction diagram illustrates a diphenyloxalate molecule reacting with a hydrogen peroxide molecule to form twophenol molecules and one 1,2-dioxetanedione molecule. The middle portionof the chemical reaction diagram illustrates that the 1,2-dioxetanedionemolecule, having an unstable strained ring, decomposes spontaneously tocarbon dioxide and releases energy that excites a dye (with the exciteddie identified as “dye*” in FIG. 2B). The bottom portion of the chemicalreaction diagram illustrates that the excited dye then releases a photonas it returns to its ground state, with “hv” representing the standardnotation referring to release of radiant energy other than heat duringthe reaction.

The wavelength of the photon that is released as the excited dye returnsto its ground state depends on the structure of a particular dye that isselected. To illustrate, different dyes may have different photonemission spectral distributions. Similarly, different photoinitiatorsmay have different photoinitiator absorbance spectral distributions. Aphoton emission spectral distribution associated with a particular dyemay be used to identify peak emission region(s), and the peak emissionregion(s) may be compared to a photoinitiator absorbance spectraldistribution associated a particular photoinitiator to determine whetherthe particular photoinitiator is sufficiently absorbent in the peakemission region(s). As such, a particular combination of a dye and aphotoinitiator may be selected such that a wavelength of a photonemitted when the excited dye returns to its original state issatisfactory to excite the photoinitiator to initiate polymerization ofthe monomers. In some cases, the emission peak(s) in a photon emissionspectral distribution associated with a particular dye may be comparedto a spectral distribution associated with a light source (e.g., amercury arc lamp) that is typically utilized to photo-cure apolymer/adhesive. A photoinitiator (or multiple photoinitiators) may beidentified as satisfactory for the individual emission peaks in thespectral distribution associated with the light source.

As an illustrative, non-limiting example, the dye may be9,10-diphenylanthracene which has a marked emission peak at 405 nm andappreciable emission at 436 nm. In this case, an illustrative,non-limiting example of a photoinitiator with a satisfactoryphotoinitiator absorbance spectral distribution is Ciba® IRGACURE™ 784from Ciba Specialty Chemicals Inc. It will be appreciated that numerouscombinations of dyes and photoinitiators may be suitable to initiatepolymerization of a particular set of monomers (e.g., acrylatemonomers).

Thus, FIGS. 2A and 2B illustrate an example of a light generatingmicrocapsule of the present disclosure before application of acompressive force (FIG. 2A) and after application of the compressiveforce (FIG. 2B). As described further herein, the chemiluminescentreaction within the light generating microcapsule may generate lightthat is within a particular wavelength range that is satisfactory totrigger a particular photoinitiator to initiate polymerization of aparticular set of monomers that fill a crack in a self-healing polymericmatrix material.

FIG. 3A illustrates a cross-sectional view 300 of selected portions ofthe article of manufacture 100 of FIG. 1 at a first stage of propagationof a crack 302 in the self-healing polymeric matrix material 104. InFIG. 3A, a monomer mixture 304 (that includes the monomers and thephotoinitiator, as previously described herein) is shown as beingencapsulated within an individual monomer mixture microcapsule 306 ofthe plurality of monomer mixture microcapsules 106 depicted in FIG. 1.Thus, the first stage of propagation of the crack 302 depicted in FIG.3A shows the encapsulation of the monomer mixture 304 prior to ruptureof the individual monomer mixture microcapsule 306.

FIG. 3B illustrates a cross-sectional view 310 of selected portions ofthe article of manufacture 100 of FIG. 1 at a second stage ofpropagation of the crack 302, resulting in microcapsule rupture 312 ofthe individual monomer mixture microcapsule 306 depicted in FIG. 3A.FIG. 3B further illustrates that the microcapsule rupture 312 enablesthe monomer mixture 304 to fill the crack 302 in the self-healingpolymeric matrix material 104. Thus, the second stage of propagation ofthe crack 302 depicted in FIG. 3B shows the monomer mixture 304 fillingthe crack 302 prior to rupture of the individual light generatingmicrocapsule 202.

FIG. 3C illustrates a cross-sectional view 320 of selected portions ofthe article of manufacture 100 of FIG. 1 at a third stage of propagationof the crack 302, resulting in application of a compressive force 322 tothe individual light generating microcapsule 202 of the plurality oflight generating microcapsules 102 dispersed in the self-healingpolymeric matrix material 104. The compressive force 322 triggers thechemiluminescent reaction (identified by the reference character 222 inFIG. 3C) within the light generating microcapsule 202, causing thephotoinitiator in the monomer mixture 304 to initiate polymerization ofthe monomers of the monomer mixture 304 within the crack 302. FIG. 3Cillustrates that polymerization of the monomer mixture 304 results information of a polymerized material 324 within the crack 302, therebypreventing further propagation of the crack 302.

Thus, FIGS. 3A-3C illustrate an example in which propagation of a crackthat is formed in a self-healing polymeric matrix material (see FIG. 3A)causes a monomer mixture microcapsule to rupture and release anencapsulated monomer mixture into the crack (see FIG. 3B). FIG. 3Cillustrates that further propagation of the crack results in applicationof a compressive force to a light generating microcapsule that triggersa chemiluminescent reaction within the light generating microcapsule.The emitted light has sufficient energy to excite a photoinitiator (inthe monomer mixture that has filled the crack, as shown in FIG. 3B) toinitiate polymerization (e.g., free radical polymerization) of themonomers in the crack. FIG. 3C further illustrates that polymerizationof the monomers results in the formation of a polymerized materialwithin the crack, thereby preventing further propagation of the crack.

FIG. 4 is a flow diagram illustrating, through stages 4(a) to 4(f), anexample of a method 400 of producing a multiple-compartment microcapsulehaving a shell-in-shell architecture with an inner shell containedwithin an outer shell, where the inner shell is adapted to rupture inresponse to application of a compressive force to cause achemiluminescent reaction within the microcapsule, according to someembodiments. In each of the stages 4(a)-4(f), the structure is shown ina cross-sectional side view. The microcapsule produced in FIG. 4 maycorrespond to the multiple-compartment microcapsule 202 depicted in FIG.2A that represents one of the light generating microcapsules 102depicted in FIG. 1.

Referring to FIG. 4, and according to an embodiment, the shell-in-shellmicrocapsules can be made using any reactants and oxidants of anychemiluminescent reaction (identified as “First Reactant(s)” and “SecondReactant(s)” in FIG. 4). For example, First Reactant(s) may be a dye anddiphenyl oxalate, and Second Reactant(s) may be an oxidant such ashydrogen peroxide. Once the inner shell ruptures, the reactants mix andemit photons. One skilled in the art will understand that a variety ofchemiluminescent reactants can be used. Both the First Reactant(s) andthe Second Reactant(s) may comprise one or more chemicals, particles,and combinations thereof.

In the example depicted in FIG. 4, magnetic nanoparticles are used inoperation 402 for incorporation into the “inner core” CaCO₃microparticles (shown at stage 4(b)). Magnetic nanoparticles areincorporated into the “inner core” CaCO₃ microparticles for the purposeof subsequently magnetically isolating the product prepared in operation406 (i.e., ball-in-ball CaCO₃ microparticles) from a coproduct (i.e.,single core CaCO₃ microparticles). The magnetic nanoparticles may be,for example, Fe₃O₄ (also referred to as “magnetite”) nanoparticles,cobalt ferrite nanoparticles or other magnetic nanoparticles known inthe art. In a particular embodiment, the magnetic nanoparticles may havea diameter in a range of approximately 6 nm to 25 nm.

An example of a technique of preparing magnetite nanoparticles follows.A 5 mol/l NaOH solution is added into a mixed solution of 0.25 mol/lferrous chloride and 0.5 mol/l ferric chloride (molar ratio 1:2) untilobtaining pH 11 at room temperature. The slurry is washed repeatedlywith distilled water. Then, the resulting magnetite nanoparticles aremagnetically separated from the supernatant and redispersed in aqueoussolution at least three times, until obtaining pH 7. A typical averagediameter of the resulting magnetite nanoparticles may be about 12 nm.

The microparticle system described with respect to FIG. 4 is based onCaCO₃ microparticles that are hardened by formation of a polyelectrolytemultilayer around the CaCO₃ microparticles. The method 400 begins bypreparing spherical calcium carbonate microparticles in which magnetitenanoparticles and First Reactant(s) (e.g., diphenyl oxalate and a dye,such as 9,10-diphenylanthracene) are immobilized by coprecipitation(operation 402). For example, 1M CaCl₂ (0.615 mL), 1M Na₂CO₃ (0.615 mL),1.4% (w/v) magnetite nanoparticle suspension (50 μL), First Reactant(s)(0.50 mg dye and 133 mg oxalate), and deionized water (2.450 mL) may berapidly mixed and thoroughly agitated on a magnetic stirrer for about 20seconds at about room temperature. After the agitation, the precipitatemay be separated from the supernatant by centrifugation and washed threetimes with water. One of the resulting CaCO₃ microparticles is shown atstage 4(b).

The diameter of the CaCO₃ microparticles produced with a reaction timeof 20 seconds is about 4 μm to about 6 μm. Smaller CaCO₃ microparticlesare produced if the reaction time is reduced from about 20 seconds toabout several seconds. One skilled in the art will appreciate that othermagnetic nanoparticles may be used in lieu of, or in addition to, themagnetite. For example, cobalt ferrite nanoparticles may also be used.

In this example, the fabrication of polyelectrolyte capsules is based onthe layer-by-layer (LbL) self-assembly of polyelectrolyte thin films.Such polyelectrolyte capsules are fabricated by the consecutiveadsorption of alternating layer of positively and negatively chargedpolyelectrolytes onto sacrificial colloidal templates. Calcium carbonateis but one example of a sacrificial colloidal template. One skilled inthe art will appreciate that other templates may be used in lieu of, orin addition to, calcium carbonate.

The method 400 continues by LbL coating the CaCO₃ microparticles(operation 404). In operation 404, a polyelectrolyte multilayer (PEM)build-up may be employed by adsorbing five bilayers of negative PSS(poly(sodium 4-styrenesulfonate); Mw=70 kDa) and positive PAH(poly(allylamine hydrochloride); Mw=70 kDa) (2 mg/mL in 0.5M NaCl) byusing the layer-by-layer assembly protocol. For example, the CaCO₃microparticles produced in operation 402 may be dispersed in a 0.5M NaClsolution with 2 mg/mL PSS (i.e., polyanion) and shaken continuously for10 min. The excess polyanion may be removed by centrifugation andwashing with deionized water. Then, 1 mL of 0.5M NaCl solutioncontaining 2 mg/mL PAH (i.e., polycation) may be added and shakencontinuously for 10 min. The excess polycation may be removed bycentrifugation and washing with deionized water. This deposition processof oppositely charged polyelectrolyte may be repeated five times and,consequently, five PSS/PAH bilayers are deposited on the surface of theCaCO₃ microparticles. One of the resulting polymer coated CaCO₃microparticles is shown at stage 4(c).

The thickness of this “inner shell” polyelectrolyte multilayer may bevaried by changing the number of bilayers. Generally, it is desirablefor the inner shell to rupture while the outer shell remains intact.Typically, for a given shell diameter, thinner shells rupture morereadily than thicker shells. Hence, in accordance with some embodimentsof the present disclosure, the inner shell is made relatively thincompared to the outer shell. On the other hand, the inner shell must notbe so thin as to rupture prematurely.

The PSS/PAH-multilayer in operation 404 is but one example of apolyelectrolyte multilayer. One skilled in the art will appreciate thatother polyelectrolyte multilayers and other coatings may be used in lieuof, or in addition to, the PSS/PAH-multilayer in operation 404.

The method 400 continues by preparing ball-in-ball calcium carbonatemicroparticles in which Second Reactant(s) (which can be any suitableoxidant, including hydrogen peroxide) is immobilized by a secondcoprecipitation (operation 406). “Immobilize” means “removing fromgeneral circulation, for example by enclosing in a capsule.” Theball-in-ball CaCO₃ microparticles are characterized by a polyelectrolytemultilayer that is sandwiched between two calcium carbonatecompartments. In operation 406, the polymer coated CaCO₃ microparticlesmay be resuspended in 1M CaCl₂ (0.615 mL), 1M Na₂CO₃ (0.615 mL), anddeionized water (2.500 mL) containing hydrogen peroxide (1 mg), rapidlymixed and thoroughly agitated on a magnetic stirrer for about 20 secondsat about room temperature. After the agitation, the precipitate may beseparated from the supernatant by centrifugation and washed three timeswith water. The second coprecipitation is accompanied by formation of acoproduct, i.e., single core CaCO₃ microparticles that contain onlyhydrogen peroxide. Hence, the resulting precipitate represents a mixtureof ball-in-ball CaCO₃ microparticles and single core CaCO₃microparticles. The ball-in-ball CaCO₃ microparticles, which aremagnetic due to the immobilized magnetite nanoparticles in the innercompartment, may be isolated by applying an external magnetic field tothe sample while all of the nonmagnetic single core CaCO₃ microparticlesare removed by a few washing steps. One of the resulting ball-in-ballCaCO₃ microparticles is shown at stage 4(d).

The method 400 continues by coating the ball-in-ball CaCO₃microparticles (operation 408). In an embodiment, the outer shell wallmaterial is made of a material for the chemiluminescent photon to escapethe shell. In another embodiment, the outer shell wall material is madeof a material where the photon yield outside the wall of the outer shellwall is maximized. In an embodiment, the outer shell wall has atransmittance of at least 90%. In certain embodiments, the outer shellwall material may include natural polymeric material, such as gelatin,arabic gum, shellac, lac, starch, dextrin, wax, rosin, sodium alginate,zein, and the like; semi-synthetic polymer material, such as methylcellulose, ethyl cellulose, carboxymethyl cellulose, hydroxyethyl ethylcellulose; full-synthetic polymer material, such as polyolefins,polystyrenes, polyethers, polyureas, polyethylene glycol, polyamide,polyurethane, polyacrylate, epoxy resins, among others. In certainembodiments, the method for wrapping a core material includes chemicalmethods such as interfacial polymerization, in situ polymerization,molecular encapsulation, radiation encapsulation; physicochemicalmethods such as aqueous phase separation, oil phase separation,capsule-heart exchange, pressing, piercing, powder bed method; andphysical methods, such as spray drying, spray freezing, air suspension,vacuum evaporation deposition, complex coacervation, long and shortcentrifugation.

An example of a conventional technique of preparing the outer shellfollows, and can be accomplished at stage 4(e). A gelatin is dissolvedinto n-hexane in a water bath at about 50° C. to obtain a 6% gelatinsolution. The gelatin may optionally be swelled with deionized waterbefore the preparation of the gelatin solution. The ball-in-ball CaCO₃microparticles prepared in operation 406 are added to the gelatinsolution while stirring to form an emulsified dispersion system. The pHis then adjusted to about 3.5-3.8 using acetic acid, and then a 20%sodium sulfate solution is slowly added into the dispersion system whilemaintaining a temperature of about 50° C. The temperature of thedispersion system is then lowered to a temperature of about 15° C. Theresult is a colloid of gelatin coated ball-in-ball CaCO₃ microparticles.

Generally, it is desirable for the inner shell to rupture while theouter shell remains intact so that the reactants and the reactionproducts do not contaminate the material into which themulti-compartment microcapsule is dispersed. Typically, for a givenshell diameter, thinner shells rupture more readily than thicker shells.Hence, in accordance with some embodiments of the present disclosure,the outer shell is made relatively thick compared to the inner shell.

Operation 410 is a CaCO₃ extraction. In operation 410, the CaCO₃ core ofthe ball-in-ball CaCO₃ microparticles may be removed by complexationwith ethylenediaminetetraacetic acid (EDTA) (0.2M, pH 7.5) leading toformation of shell-in-shell microcapsules. For example, the gelatincoated ball-in-ball CaCO₃ microparticles produced in operation 408 maybe dispersed in 10 mL of the EDTA solution (0.2M, pH 7.5) and shaken forabout 4 h, followed by centrifugation and re-dispersion in fresh EDTAsolution. This core-removing process may be repeated several times tocompletely remove the CaCO₃ core. The size of the resultingshell-in-shell microcapsules ranges from about 8 μm to about 10 μm, andthe inner core diameter ranges from about 3 μm to about 5 μm. One of theresulting shell-in-shell microcapsules is shown at stage 4(f). Dependingon the application of use, the shell-in-shell microcapsule can have arange of about 0.5 μm to about 200 μm.

As noted above, the fabrication of polyelectrolyte capsules in themethod 400 of FIG. 4 is based on the layer-by-layer (LbL) self-assemblyof polyelectrolyte thin films. One skilled in the art will appreciatethat a multi-compartment microcapsule for light generation in accordancewith some embodiments of the present disclosure may be produced by otherconventional multi-compartment systems, such as polymeric micelles,hybrid polymer microspheres, and two-compartment vesicles.

As noted above, one skilled in the art will understand that variouschemiluminescent reactants and oxidants can be used. Moreover, themulti-compartment microcapsule can utilize various chemiluminescentreactions. The chemistry used in chemiluminescent reactions is a maturetechnology, and those skilled in the art will know that additionalmaterials can be further added to the multi-compartment microcapsule.For example, enhancing reagents such as alkyl dimethyl benzyl quaternaryammonium salt may be added to the reactants.

The photon-emitting reactants may be chosen to be inert with respect tothe material of the microcapsule walls, or an isolating barrier within amicrocapsule when the reactants are not in contact. The photon-emittingreactants also may be chosen to be inert with respect to the outermicrocapsule wall when the reactants are in contact, or such that thechemical products of the reaction are inert with respect to the outermicrocapsule wall, and any remnants of the inner microcapsule wall orbarrier.

An amount of the first reactant(s) and an amount of the secondreactant(s) may be determined. The amounts may be determined from thetotal amount of the reactants required to produce a desired amount ofphotons, the ratio of each reactant according to a reaction equation,the desired dimensions of the microcapsule, and the manner of isolatingthe reactants within the capsule. For example, a microcapsule may bedesired having a maximum dimension less than or equal to a desired finalthickness of less than 0.5 microns, and the amount of reactants may bechosen corresponding to the volume available within a microcapsuleformed according to that dimension.

Thus, FIG. 4 illustrates an example of a process of forming amultiple-compartment microcapsule having an inner shell adapted torupture when exposed to a compressive force in order to trigger achemiluminescent reaction within the microcapsule. Themultiple-compartment microcapsule formed according to the processdepicted in FIG. 4 may correspond to the multiple-compartmentmicrocapsule 202 illustrated and described further herein with respectto FIG. 2A.

It will be understood from the foregoing description that modificationsand changes may be made in various embodiments of the present inventionwithout departing from its true spirit. The descriptions in thisspecification are for purposes of illustration only and are not to beconstrued in a limiting sense. The scope of the present invention islimited only by the language of the following claims.

What is claimed is:
 1. A self-healing polymeric material comprising: a polymeric matrix material; wherein dispersed within the polymeric matrix material is a mixture of materials that includes monomers and a photoinitiator; and a plurality of light generating microcapsules dispersed in the polymeric matrix material, each light generating microcapsule of the plurality of light generating microcapsules encapsulating multiple reactants that undergo a chemiluminescent reaction, wherein each light generating microcapsule comprises an outer shell and an inner shell, wherein the chemiluminescent reaction generates a photon having a wavelength within a particular emission range that is consistent with an absorption range of the photoinitiator and wherein the chemiluminescent reaction occurs without rupture of the outer shell of the light generating microcapsules.
 2. The self-healing polymeric material of claim 1, wherein a crack in the polymeric matrix material causes migration of the monomers and photoinitiator into the crack.
 3. The self-healing polymeric material of claim 2, wherein further propagation of the crack in the polymeric matrix material results in application of a compressive force to a light generating microcapsule of the plurality of light generating microcapsules, the compressive force triggering the chemiluminescent reaction within the light generating microcapsule.
 4. The self-healing polymeric material of claim 3, wherein the photon generated within the light generating microcapsule exits the light generating microcapsule into the crack to trigger the photoinitiator to initiate a polymerization reaction of the monomers within the crack, the polymerization reaction resulting in formation of a polymeric material that seals the crack.
 5. The self-healing polymeric material of claim 4, wherein the photoinitiator includes a free radical initiator, and wherein the polymerization reaction includes a free radical polymerization reaction.
 6. The self-healing polymeric material of claim 1, wherein the monomers include acrylate monomers.
 7. The self-healing polymeric material of claim 1, wherein the chemiluminescent reaction includes excitation of a dye from a ground state to an excited state and subsequent release of the photon upon relaxation from the excited state to the ground state.
 8. The self-healing polymeric material of claim 7, wherein excitation of the dye is caused by energy released during decomposition of a 1,2-dioxetanedione molecule.
 9. The self-healing polymeric material of claim 8, wherein a chemical reaction of a diphenyl oxalate molecule with a hydrogen peroxide molecule results in formation of the 1,2-dioxetanedione molecule.
 10. The self-healing polymeric material of claim 7, wherein the dye includes 9,10-diphenylanthracene.
 11. The self-healing polymeric matrix material of claim 1, wherein each light generating microcapsule includes a multiple-compartment microcapsule that comprises: a first compartment that contains a first reactant of the multiple reactants; a second compartment that contains a second reactant of the multiple reactants; and wherein the inner shell is an isolating structure separating the first compartment from the second compartment, the isolating structure adapted to rupture in response to application of a compressive force to cause the first reactant and the second reactant to undergo the chemiluminescent reaction.
 12. The self-healing polymeric matrix material of claim 11, wherein the multiple-compartment microcapsule includes a shell-in-shell microcapsule and the inner shell is contained within the outer shell, wherein the inner shell encapsulates the first compartment, wherein the outer shell encapsulates the second compartment.
 13. The self-healing polymeric matrix material of claim 12, wherein the outer shell comprises a polymer, and wherein the outer shell has a transmittance value of at least 90% for the wavelength within the particular emission range.
 14. The self-healing polymeric matrix material of claim 13, wherein the polymer comprises gelatin, arabic gum, shellac, lac, starch, dextrin, wax, rosin, sodium alginate, zein, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, hydroxyethyl ethyl cellulose, polyolefins, polystyrenes, polyethers, polyesters, polyureas, polyethylene glycol, polyamides, polyimides, urea-formaldehydes, polyurethane, polyacrylate, epoxy resins, and combinations thereof. 